From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 59E213164D0; Thu, 19 Feb 2026 02:05:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771466715; cv=none; b=JQpV2X65EL0JjbHY6MjZmwmWHBf/nSnJOu0cQCQvzCX2psd+M5kzJ8qj345J2hG6JNK5NBbB2vNBaIksYMAy/34ISfoHvN1LUTudDy4ionUaj9vhFJr6KaT4eqAbZhZcNGn4ggG2fsOyLGc8/zWUewI+N5AK2GzUpYDAqyfQWOI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771466715; c=relaxed/simple; bh=CJhzGH3sAa0J4fOkP0CpNIISd/xcJc3TRjy4YycFwTY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=Grnh7XjYWSiIIv/52c9mzI5oifRR3SN7CT/9R6AQzqnS+GdQJYdCy7Ef4bykJaphigHkssX6MV7zlpm3AVdwsTYvagrER/iEFWJIk6n+0KV9H8UvAB0Dsf/pD0gJ7nc5lWRHN3k6GOvaTpGt4UekTHL0Vi+oGRZRMp823tP7R5w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=n74SW63m; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="n74SW63m" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 00B13C19425; Thu, 19 Feb 2026 02:05:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771466715; bh=CJhzGH3sAa0J4fOkP0CpNIISd/xcJc3TRjy4YycFwTY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=n74SW63m3g2vdXmFe3PM5znz6KRPmNRYMfgHOkvKjEl98qnQTDDxvmylU6XbUbAXg lUdFncUSLM1ksgLt6Odpy0PbmiQaHrtGuGmuh89xzmS9EORRxSz2MMKLf7ZmbxGGuc NloIThis473MS7v/DH5MkWbffUHpZNHXIJt4gVg6neLGGxKIhmPpYEBAdmfX9cb5Tv /mAD+Hx9iaJvTjlGHOtnbrHRxbiXJj+RU54z2Ih3MwFJ7QRGq0NXCN1YBN7XV6jA72 kDGj6YPpYX5EfuWm7cHJDIahKfDHgHIeZkhjKffXO/9aa9wa5aozGF0UEn16vFabmX QfO3OysVSxRRg== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: =?UTF-8?q?Cl=C3=A9ment=20Le=20Goffic?= , =?UTF-8?q?Cl=C3=A9ment=20Le=20Goffic?= , Amelie Delaunay , Vinod Koul , Sasha Levin , mcoquelin.stm32@gmail.com, alexandre.torgue@foss.st.com, dmaengine@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH AUTOSEL 6.19-6.1] dmaengine: stm32-mdma: initialize m2m_hw_period and ccr to fix warnings Date: Wed, 18 Feb 2026 21:04:16 -0500 Message-ID: <20260219020422.1539798-40-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260219020422.1539798-1-sashal@kernel.org> References: <20260219020422.1539798-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.19.2 Content-Transfer-Encoding: 8bit From: Clément Le Goffic [ Upstream commit aaf3bc0265744adbc2d364964ef409cf118d193d ] m2m_hw_period is initialized only when chan_config->m2m_hw is true. This triggers a warning: ‘m2m_hw_period’ may be used uninitialized [-Wmaybe-uninitialized] Although m2m_hw_period is only used when chan_config->m2m_hw is true and ignored otherwise, initialize it unconditionally to 0. ccr is initialized by stm32_mdma_set_xfer_param() when the sg list is not empty. This triggers a warning: ‘ccr’ may be used uninitialized [-Wmaybe-uninitialized] Indeed, it could be used uninitialized if the sg list is empty. Initialize it to 0. Signed-off-by: Clément Le Goffic Reviewed-by: Clément Le Goffic Signed-off-by: Amelie Delaunay Link: https://patch.msgid.link/20251217-mdma_warnings_fix-v2-1-340200e0bb55@foss.st.com Signed-off-by: Vinod Koul Signed-off-by: Sasha Levin --- LLM Generated explanations, may be completely bogus: I can see `sg_len` is passed from the DMA framework's `prep_slave_sg` callback. While the DMA framework generally doesn't call this with `sg_len == 0`, there's no explicit guard against it in this function. The `stm32_mdma_alloc_desc` with `sg_len == 0` might succeed (allocating a descriptor with 0 nodes), allowing execution to reach `stm32_mdma_setup_xfer` with an empty list. ### Verification - **Read the actual code**: Confirmed `ccr` is used at lines 777-779 after the for_each_sg loop, and if `sg_len == 0`, `ccr` is never initialized by `stm32_mdma_set_xfer_param()`. - **Caller analysis**: `stm32_mdma_setup_xfer` is called from `stm32_mdma_prep_slave_sg` at line 809 with `sg_len` from the DMA framework - no explicit guard for `sg_len == 0`. - **m2m_hw_period**: Confirmed at lines 737-738 and 749-750/758-759 that it's only used when `chan_config->m2m_hw` is true (false positive warning). - **Risk assessment**: The change is a trivial initialization, zero regression risk. - **Could NOT verify**: Whether any real-world code path actually passes `sg_len == 0` to `prep_slave_sg` (unverified, but defensive initialization is correct practice). ### Conclusion This is a very low-risk fix that: 1. Silences compiler warnings (useful for clean builds) 2. Fixes a real (if potentially rare) uninitialized variable bug for `ccr` The fix is trivially correct, one line, zero regression risk, and fixes a genuine code correctness issue. While it's borderline because the primary framing is "fix warnings" and the affected driver is STM32-specific, the `ccr` uninitialized variable is a real bug that could cause DMA hardware misconfiguration, and the fix has absolutely no downside. **YES** drivers/dma/stm32/stm32-mdma.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/dma/stm32/stm32-mdma.c b/drivers/dma/stm32/stm32-mdma.c index 080c1c725216c..b87d41b234df1 100644 --- a/drivers/dma/stm32/stm32-mdma.c +++ b/drivers/dma/stm32/stm32-mdma.c @@ -731,7 +731,7 @@ static int stm32_mdma_setup_xfer(struct stm32_mdma_chan *chan, struct stm32_mdma_chan_config *chan_config = &chan->chan_config; struct scatterlist *sg; dma_addr_t src_addr, dst_addr; - u32 m2m_hw_period, ccr, ctcr, ctbr; + u32 m2m_hw_period = 0, ccr = 0, ctcr, ctbr; int i, ret = 0; if (chan_config->m2m_hw) -- 2.51.0